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This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.

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A326301 The number of rectangular free polyominoes with n cells where no 4 cells meet at a point.

Original entry on oeis.org

1, 2, 3, 8, 19, 54, 159, 511, 1676, 5685, 19512
Offset: 1

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Author

R. J. Mathar, Oct 17 2019

Keywords

Comments

Obtained from the polyominoes of A056780 by discarding the polyominoes that contain 2 X 2 subblocks of 4 cells. One may call this the Tatami version of the free rectangular polyominoes.
This might also be considered a well-defined (or corrected?) version of A002369.

Examples

			From the A056780(4) = 9 polyominoes the one with the 2 X 2 bounding box is not counted, giving a(4)=8.
From the A056780(5)=21 polyominoes, 2 are not counted:
L
LL      and     LL
LL              LLL

Crossrefs

Cf. A056780, A002369.
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Started in 1964 by Neil J. A. Sloane | Maintained by The OEIS Foundation Inc.

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